Problem: The sum of $6$ consecutive odd numbers is $156$. What is the first number in this sequence?
Explanation: Call the first number in the sequence $x$ The next odd number in the sequence is $x + 2$ The sum of the $6$ consecutive odd numbers is: $x+ (x + 2)+ (x + 4)+ (x + 6)+ (x + 8)+ (x + 10) = 156$ $6x + 30= 156$ $6x = 126$ $x = 21$ Thus, the first number is $21$.